Evolution of the inferred power index estimated on averaged periodograms of one-day solar subseries. From left to right: index evaluated for (a) the high-frequency region, (b) the p-modes region, (c) the granulation region, and (d) the lowest frequency region. Each color corresponds to an SPM channel. In region (c), the index obtained on the HMI solar observations discussed in Sect. 3.1 is shown by the horizontal black line (with the 1σ uncertainties in gray). This index results from the averaged periodogram computed using the 91 one-day subseries that have been selected during the period of a solar minimum (2017–2019).